There are several schools of thought when it comes to Power Supplies and voltage rails. One group of people insists that you need a large number of 12v rails in order to ensure stability across the entire platform. The other group states that a single or a couple of larger 12v rails perform better than many rails with lower amperage. Today we are looking at the Zalman 850W PSU and will put this debate to the test as this PSU has a total of six 12v rails that each provides 18A and a total of 720W across the 12v lines. We will be putting this PSU to the test in the most demanding system we've built to date and manage to consistently pull 650W in a full-load situation. This PSU sweats, but does it break down and beg for mercy? Keep on reading to find out.

PSU Box

First Impressions:

The PSU comes in a very nice retail package and proudly boasts a 3 year warranty among other features. This PSU features 80%+ Power Efficiency rating - meaning that if you're drawing 800W from the wall, the PSU is actually only providing a little better that 660W to your system. This is something to keep in mind if you're using a Watt Meter on the input side of things. Coming from Zalman we already expect this unit to be quiet, and this is due to a nice quiet 14cm fan as well as some heatpipes inside the unit.

Inner Boxes

Wrong Country

Inside the main box are a couple of smaller boxes. The box on the top is larger and contains a well protected PSU. The box on the bottom has is full of cables, including a fan connector that allows you to run system fans at either 12v or 5v. They also include a power cable that apparently was made for a different country - continent rather, other than North America. Hopefully this PSU works and detects input voltage, as there is no switch to select between 110v and 220v.

PSU First Look:

This PSU is a little longer than other standard ATX units and if you've got a really crammed case it may pose some problems. The overall length is 21cm long, but it should fit in many mid-tower cases without issues. If you have a top exhaust fan, measure before you purchase this unit.

Attached Cables

Rear Grill

Fan Outside

Modular Connectors

The ZM850-HP has a very nice finish and looks very nice. As you can see in the first picture above, this is not a completely modular unit at all. In fact, if you've got a very basic system you won't even need to plug in any cables. The cables that are hard-wired to the unit may be enough for some people. If you are buying this unit though, and want as many as six 12v rails, you've probably got more gear.

The rear of the unit is well ventilated and you can see the heatpipe laden heatsinks through this wide open grill. The entire unit is cooled by a very quiet 14cm fan that we clocked at 780rpm during heavy use. This provides adequate cooling with virtually no noise - which is what we expected from Zalman. On the inside end of the PSU you can see the different modular connectors as well as a switch. This switch is actually a Standby Noise Filter Switch. I'm not sure why Zalman wouldn't make the standby voltage "low noise" by default, but apparently there is a reason and you can enable or disable low electrical noise when in standby.

On the next page we'll take a look at PSU features and specifications.